Kinematics and geochronology of multistage ductile deformation along the eastern Alxa block,NW China: New constraints on the relationship between the North China Plate and the Alxa block |
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| Institution: | 1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Departamento de Geología, Universidad de Huelva, Campus del Carmen, Huelva 21071, Spain;3. China University of Geosciences, Beijing 100083, China;1. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China;2. Department of Geology and Planetary Science, University of Pittsburgh, 4107 O''Hara Street, Pittsburgh, PA 15260-3332, USA;3. Department of Geology, Northwest University, Xi''an 710069, China;1. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China;2. Department of Geology and Planetary Science, University of Pittsburgh, 4107 O''Hara Street, Pittsburgh, PA 15260-3332, USA;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, Guangdong 510640, China;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China |
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| Abstract: | The NE-trending Bayanwula Shan–Lang Shan is an important tectonic belt lying between the North China Plate (NCP) to the east and the Alxa block to the west. An understanding of its nature and the timing of deformation are essential to understand the relationship between the NCP and the Alxa block. Two phases of ductile deformation have been observed in this belt. Large-scale top-to-the-west ductile thrusting characterized the early deformation in the Bayanwula Shan–Lang Shan. Nearly east–west trending quartz stretching lineations and lineations formed by amphibole and biotite are well developed. Different types of sheath and oblique folds with east–west trending fold hinges are also developed in the region. The shear strain of this ductile thrust is up to 17. The ductile deformation may have resulted from the top-to-the-west thrusting of the northern part of the NCP over the Alxa block, and may have occurred ca. 351 Ma (biotite 40Ar/39Ar age). Later ductile deformation was expressed as NE-trending sinistral shear along the entire Bayanwula Shan–Lang Shan and likely occurred ca. 250 Ma (biotite and muscovite 40Ar/39Ar ages); this shear may have resulted from the collision between the Yangtze and North China plates to the south during the Triassic. Combined with recently obtained detrital zircon U–Pb ages for the area, the ductile deformation events in the eastern Alxa block indicate that the block may not have been part of the NCP, at least before the end of the Devonian. Both blocks were located in the Paleo-Asian Ocean during the Paleozoic and collided or amalgamated with each other at the end of the Devonian. |
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| Keywords: | Alxa block North China Plate Ductile thrust Sinistral ductile shear Triassic |
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